Magnetron cathode structures



Sept. 27, 1966 zwo ET AL MAGNETRON CTHODE STRUCTURES 5 Sheets-Sheet 1Filed May 25. 1961 l/VVE/WOS REN ZWOBADA ENRICO PI'ATTI JACQUES BEAL'REMI JUILLERAT Sept. 27,196 R. ZWOBADA ETAL 3,275,366

' MAGNETRON CATHODE STRUCTURES Filed May 25, 1961 5 SheetsSheet 2 F:3/NVENOS REN ZWOBADA ENRICO PIATTI JACQUES BEAL REMI JUILLERT Sept. 27,1966 R.ZWOBADA ETAL MAGNETRON CATHODE STRUCTURES Filed May 25, 1961 5Sheets-Sheet 5 INVEA/7OS REN ZWOBADA ENRICO PIATTI JACQUES BEAL REMIJUILLERT United States Patent 3,275,866 MAGNEIRON CAIHDE STRUCTURES RenZwobada, Enrico Piatfi, Jacques Beal, and Rerm Juillerat, all of Paris,France, assignors to Societe Lignes'Telegraphiques et Telephoniques,Paris, France, a joint-stock company of France Filed May 25, 1961, Ser.No. 126,370 Claims priority, application France, June 14, 1960,

829,880; Oct.3l, 1960, 842,663; Apr. 27, 1961,

6 Claims. (Cl. 313-37 The invention relates to improvernents in highfrequency, high power magnetrons and bears especially on the tubestructure. As mentioned in French Patent No. 1,104,932 of May 19, 1954,the main problem in magnetrou manufacture is precise positioning of thecathode with respect to the anode block. In the above mentioned patentis described a magnetron structure designed in order to make cathodecentering casier during tube manufacture and to reduce misalignnmentwhich might occur during the tube lite. According -to the abovementioned invention, cathode centering with respect to the anode blockis visually controlled during tube assembly. An especially designedsupporting part is provided to allow setting of the pole piece withoutrequiring any further high temperature heating which may affect cathodecenter- It has been described in French Patent No. 1,200,355 bf April23, 1958, the particular problems to be 301ved in manufacturing a highpower, very high frequency magnetrou. One of the main difliculties liesin eliminating a large quantity of heat through the cathode structure,combined with the necessary heating of the cathode by an external sourcein order to bring the cathode coating at thC right temperature forinitiating oscillation. The cathode structure which is described in thelast mentioned patent is a cylindrical unit which supports at one endthe heater and, at the other end, the cooling device, the emissivecoating being located inbetween on the cylinder. Such a structure hasproved to be very reliable and to provide a long lifetime. As shown inthe dfawing appended to this patent, the cathode structure is onlysnpported at one end, the heater end is not connected to any solid partof the tube envelope. This design Will not provide for suflicientmechanical stability when the tube is submitted to high vibration oracceleration since conditions may happen when the cathode structure willvibrate thereby disturbing normal tube operation.

In order to improve the tube ruggedness, it has been proposed to fix thecathode cylinder at both ends. Such a design is vrydifiicult tomanufacture. Indeed, during the tube lite, the cathode assembly issubmitted to numer, ous thermal cycles which cause alternate expansionsand contractions and it is therefore very difiicult to fix the cathodestructure at both ends 10 parts sufficiently solid to provide formechanical rigidity without excessive stresses being developed in thecathode structure. On the other hand, the unitary cathode structure ismetallic and the end to be housed will be set at very high potentialduring operation. The design of the engaging part is thereforeditficult.

The object of the present invention consists in a magnatron structurewith a mechanical stability improved over the structure described inPatent 1,200,355 but still presenting the same advantagesas suchstructure especially with respect to evacuation of heat from the cathodestructure when the magnetron is operated at high power level.

An0ther object of the invention consists in a cathode structure whichallows for high precision centering of the cathode in the anode blockwithout requiring a specially Patented Sept. 27, 1966 designed part toallow for the setting of the second polep1ece.

It is an object of the invention to provide for a magnetron structure inwhich both the cathode hat diameters may be larger than the anode cavitydiameter.

It is an object of the present invention to provide means foreliminating any stress which may occur due to thermal expansion of thecathode structure during tube operation.

It is another object of the invention to provide for means to adjust thecathode position with respect -to the anode block after the tube isassembled.

It is an object of the invention to allow for the reductien et thenumber of dielectric to metal seals in the tube envelope.

The present invention will be readily understood by referenCe to thefollowing description and the appended V drawings which represent fourembodiments of magnovention with a welded cathode structure.

part 1 and an upper part 1".

FIGURE 4 shows a complete tube structure incorporating means foradjusting cathode Centering atter tube assembly.

The cylindrical cathode structure 1 consists of a lower Emissive coating2 is deposited near the upper end of 1 which is terminated at one end bya centering finger 3 and connected at the other end to the coolingdevice 4 of the type described in abovementioned French Patent No.1,200,355. Such device is designed for liquid cooling. Any other type ofcooling device such as a set of blades for air cooling may be used. Theanode bloc-k is shown at 5. It is brazed or welded t0 pole pieces 6 and6 as is well known. The lower part 1 of the cathode structure is fixedto the lower pole piece 6 by means of the dielectric ring 7 which issealed or brazed to pole piece 6 and t0 1 by metallic sealing rings 7'and 7. Cathode part 1 houses the heater 14 and is terminated at itslower end by a centering fiange 109 (cf. FIGURE 2B). It is positionedwith respect to upper pole piece 6" by the dielectric ring 13 sealed orbrazed by means of metal sealing rings 13 and 13". Part 1" consistsmainly of fiange 9.10, cylinder 11 and tube 12. It can be centered withprecision with respect to anode block 5 under visual control from thelower part of the structure. It is then assembled by sealing ring 13 t013 and 13" and brazing 13" to the upper pole piece 6" and ring 13' totube 12 through L profiled ring 12'. Filament 14 is connected at itslower end 15 to fiange 10 and at the upper end 16 to the annular output17 through stem 17. Filament connection is electrically insulated fromthe cathode by the dielectric ring 18. The tube envelope is completed bysealing on the insulating glass cup 19 which is the exhaust connection.Heater current flows from 17 to stem 17 which is in conductiverelationship with the upper end of filament 14. The second filamentconnection may be taken at 12 or at the lower end of the cathodestructure. It is also the cathode D.C. connection. Cylinder 11 acts as athermal screen between filament 14 and the tube envelope (13"13, etc.).

When part 1" is positioned, centering finger 3 of the lower cathode partis engaged in the fiange 10 the internal face in which has been highprecision machined. In order to make assembly easier,the lower part ofinternal face of fiange 10 is round and centering finger 3 is slightlyconical. Finger 3 is free to slide in flange to take over the thermalexpansion of the cathode structure. In order to reduce friction offinger 3 against flange 10, longitudinal grooves are machined in finger3 so as to reduce the bearing surface between 3 and 10. Such groovescould also be machined in flange 10 instead of finger 3. -Cathode unit 1is made of molybdenum and 50 is fiange 10. Cathode bats are treated 50as to rednce emissivity as is well known.

FIGURE 2A shows details of the engagng terminations of parts l'and 1' ofan embodimentslighfly different from FIGURE 1. Lower part 1 is a hollowcylinder bearing cathode bats 8 and 9 which may be either. solid withthe cylinder or fastenell brazng. Emissive coating.2 is dep rted betweenthe hats. Part '1' is terminated by centering finger 3. The lowerend ofupper part 1'. consists of centering flange 10 supported by cylinder 11which acts as a thermal screen between filament 14 and the tubeenvelope.

FIGURE 2B shows details of the engagement between parts l':and 1" of thecathode corresponding to the embodiment in FIGURE 1. Flange 10 acts "asthe second cathode hat while performing also its centering function. Inthis embodiment, flange 10 is made of amon-emissive material such forexample as molybdenum carbide, tungsten carbide, tantalum carbide, orothi nitallc carbides which as is well known are non-emissive ,at thetempetaturcs encountered in the operation of tubes of this type.Centering finger 3 is preferab lymade of the same matenal as flange 10.It is thercfore nolonger unitary with the cathode part 1. Finger 3 istightened to cathode structurel according.to any method known per sebrazing, Welding, etc

FIGURE 2C shows the cathode structure as seen in a plane perpendicularto axis of the structure, the trace of which appears as X X on FIGURE2B. The upper cathode part 1 engages in finger 3, the external face ofwhich is grooved as seen at 3"in order to reduce the bearing surfacebetween finger 3 and centeringflange 10 acting also as one of thecathodehats 9..

Diameter of the cathode bats 8 and 9 (or 10 according to the embodiment)may be chosen as large as suitable to optimize the operating conditionsof the magnetron. Indeed,it is no longer limited by the internaldiameter of the anode cavity since assembly does not require passing thecathode bats through the anode cavity.

Cylinder 11 operates as a thermal screen between filament l4 and thetube envelope. It is heated at a rather high temperature and ispreferahly made of a material which will absor-b the gas which may beliberated during tube operation due to electton bombardment ordesorption 'by the anode or envelope walls. simplify the drawing theR.F. chokes which should be provided along cylinder 11 have beenomitted. They are necessary in order -to prevent -any. loss of highfrequency energy along the cathode structure which should be restrictedto the volume of the cvities between the cathode and the anode block 5.

The thickness of cylinder 11 is chosen in order to allow a sufiicientelasticity of this cylindrical part so as to allow it to be distortedunder the -ctlntrol of centering adjustment device not represented inFIGURE 1 which is operated as will be explained in relationship in.FIG-URE 4 in order to provide final adjustment of the cathode position Withrespect to the anode block.

FIGURE 3 represents the same tube structure in which free thermalexpansion of the cathode is allowed by means external to the cathodestructure and located on the tube envelope, that is at a point which iskept cool even during tube operation. The parts common to the structuresdescrihed on FIGURESI and 3 bear the same reference numbers.

During tube assembly, centering finger 3 cf part 1' is rigidly fixed inart 1" by brazing or welding to flange 10.. The upper end of cylinder 11is connected to a pair Iby welding 011 In order, to

4 of fianges 21; and 22. These flanges are made of a metal lie, sheetsuficientlythin to allow resilient deformation of the two flanges whichconstitute a mobile parallel ogram allowing free translation of thewhole cathode structure along a direction parallel to its axis. Theparallelogram defined by the radial flanges 2122 prevents any radialdisplacement of cylinder 11 therefore preserving cathode concentricty.Flanges 10, 21, 22, cylinder 11 and the centering finger 3 are machinedon the same tool fiXture so as to allow for the best concentricity whichmay be obtained. Tube assembly is made as follows: fianges 10," 21 and22 are welded t0 the upper part 1 subassembly which consiste, of flahge10, cylinder- Il, filament connection seal18 and the exhaustconnection19 (shown sealed in the figure).- The subassenflhly is then machinedanother time to obtain a :high precison inside face for flange 10. It issealed at 13' andl3 to the anode sub-assembly which comprises 5613"13 13and 7'-77". The lower part 1 of the cathode structure is mounted.andfinger- 3 is engagedin fiange 10. Welding is performed between 3 and 10and then the envelope is completed by seah'ng 7" -to 1'.

FIGURE 4 shows au embodiment of the invention in which cathodepositioning with respect to the anode block may :be adjusted after.assembly of the tube. As shown in the previous figures, thecathodestructure comprises. a lower part 1 associated with the;oolirrgdevice. 4 and terminated at its upper end by centering finger 3.

The upper part 1' of the cathode structure}houses the.

heater 14 and consistsmainly of cylinderll which acts as a thermalscreen, for the heater, andas a support for centering flange 10 in whichcentering finger.3 is fixed by screwing or any other method known perse. Cylinder 11 is terxhinated by a dielectric wafer 40 whichprovidesfor the electric insulatioh of cylinder 11 with respect to theupper part'of the tube envelope. It is therefore possible; to use theupper end of the cathode structure consisting of metallic tube 12 as oneheater output without need of insulafing seal 18 instead of outputl7 ofFIGURES 1 and 3. Free expansion of the cathode structure along itsaxis'is allowed by the elasticity of one Z- shaped thin metallic flange22 welded to the cathode structure at one end and to the anode =bloek atthe other by meansof the tubeenvelope (12"131313"6").

Adjustment of cathode position is manually controlled by means of thedevice 31 to 36 associated with the lower. This adjustment isob-- part1' of a cathode structure. tained by deformation of a thin walledresilient cylinder 31 connected at its upper end 10 the cathodestructure 1' by means of a solid ring 35 and welded at its lower end toa rigid metallic ring 34of the tube envelope. 34

bears several drilled holes in which are introduced controlscrews suchas32 and 33, the end.of which bears against cylinder 36 which belongs tothe cathode struc;

ture 1" and surrounds the cooling device 4. As willbe readily understood:by screwing *or unscrewing .screws.

32, 33, etc.,jthe lower end of cylinder 31 is displad with respect tocathode structure 1'. The upper end of cylinder 31 tends also to movethereby carrying along 1'. The whole cathode structure tends.to rotate,the center of rotation being located at the seal lbetween the cathodestructure -and flange 22'. This displacement of the whole cathodestructure will change the position.of enfissive coating 2 in the anodecavity.

Tube assembly is carried on as follows: 2

threaded and is screwed in flange 10. Solid ring 21 slides along collarl3 during this operaon. the tube envelope is completed by brazing co1lar13 to ring 21.

We claim:

1. A magnetron comprising in combination: an clongated cathode structureincluding first and second parts; a filamentary heater housed withinsaid first part; means connected to said second part affordingconnection of a cooling means thereto; an emissive coating on saidstructure adjacent said first part; at least one cathode hat integral-With said second part; an apertured anode surrounding at least theemissive portion of said structure, the aperture being of less diameterthan the diameter of said bat; pole :pieces connected to said anode; andenvelope means connected between said cathode structure and said po1epieces.

2. The combinafion defined by claim 1 in which two cathode hats areintegral with said cathode structure, one positioned on either side ofsaid emissive coating.

3. The combination defined by claim 2 in which said enveIope meansincludes resilent portions connected 13etween one of said cathode partsand said po1e pieces.

4. A magnetron comprisng in combination: an clongated cathode structureincluding first and second parts; a filament heater housed within saidfirst part; means aflording connection of a cooling device to saidsecond part; an emissive coating on said second part adjacent said firstpart; a cathode hat on said second part on one side of said emissivecoating; a centering finger on said second part on the other side ofsaid coating and extending longitudinally of said second part; acentering flange terminating said first cathode part adjacent saidsecond cathode part; an apertured anode surrounding said emissivecoating, the aperture therein being of less diameter than either saidhat or fiange external diameters; po1e pieces connected to said anode;and envelope means connected between both said cathode parts and saidpole pieces.

5. A magnetron comprising in combination: an clongated cathode structureincluding first and second parts; a filament heater housed within saidfirst part; means afiording connection of a cooling device to saidsecond par-t; an emissive coating on said second part adjacent saidfirst part; a pair of cathode bats, one on each side of said emissivecoating; an apertured anode surround ing said emissive coating, theaperture theren being of Iess diameter than said cathode bats; palepieces connected to said apertured anode; envelope means counectedbetween each of said cathode parts, said means including a resilientcylinder connected between said second cathode part and said polepieces; and adjustment means contacting said second cathode part andsaid reslient cylinder.

6. The combinafion defined by claim 5 and further including at least oneresilient part connected between said first cathode part and said polepieces.

References Cited by the Examiner UNITED STATES PATENTS 2,574,562 11/1951Hanse]l 31539.63 X 2,894,171 7/1959 Vaughan et al 31339.51

JAMES W. LAWRENCE, Przmary Examiner.

JOHN W. HUCKERT, GEORGE N. WESTBY,

Examiners. V. LAFRANCHI, Assistant Examiner.

1. A MAGNETRON COMPRISING IN COMBINATION: AN ELONGATED CATHOD STRUCTUREINCLUDING FIRST AND SECOND PARTS; A FILAMENTARLY HEATER HOUSED WITHINSAID FIRST PART; MEANS CONNECTED TO SAID SECOND PART AFFORDINGCONNECTION OF A COOLING MEANS THERETO; AN EMISSIVE COATING ON SAIDSTRUCTURE ADJACENT SAID FIRST PART, AT LEST ONE CATHOD HAT INTEGRAL WITHSAID SECOND PART; AN APERTURED ANODE SURROUNDING AT LEAST THE EMISSIVEPORTION OF SAID STRUCTURE, THE APERTURE BEING LESS DIAMETER THAN THEDIAMETER OF SAID HAT; POLE PIECES CONNECTED TO SAID ANODE; AND ENVELOPEMEANS CONNECTED BETWEEN SAID CATHODE STRUCTURE AND SAID POLE PIECES.